The present invention relates generally to fish capturing devices. and more specifically to a rotary apparatus for removing fish from a stream, river, canal or other body of water.
Earlier devices for the capture of fish have varied widely in construction and effectiveness as summarized by Conlin and Tutty in their Fisheries and Marine Service Manuscript Report #1530 of the Canadian Department of Fisheries and Oceans. W. R. Humphreys discloses a self-cleaning fish trap in a 1967 Oregon State Game Commission Report. A continuous belt moves fish upwardly along an inclined plane for discharge into a tank. The efficiency of the trap is diminished somewhat by the fish, upon sensing an obstruction, escaping in a lateral direction. Stone and Webster Engineering Corporation for the Electric Power Research Institute of Palo Alto, CA, published in 1986 a report titled Migrant Fish Protection Technologies for Hydroelectric Application, EPR: AP 4711 which provides a review of fish screening technology for hydroelectric projects.
A disadvantage common to prior apparatuses is the narrow range of water velocities under which they are effective. For example, rotary drum screens and traveling screens require low approach velocities to prevent fish impingement on the screens while other fish traps require high approach velocities of the fish for capture. In addition, known traps are cumbersome and difficult to move to new locations.
Nets and fixed screens are subject to becoming plugged with debris rendering them inoperable and injurious to fish. Rotary drum screens, mounted perpendicular to the current, while overcoming debris loading problems, are generally ineffective at guiding fish into collection systems. Rotary drum screens, positioned obliquely to the current flow, are more effective at guiding fish but rapidly lose any debris removing capability. Further, known traveling screens are mechanically complex and hence expensive to construct and maintain.
A water powered, self-cleaning debris collector in U. S. Pat. No. 3,527,349 has a porous shell that removes debris from water but discharges all water through a porous shell. A ring of turbine blades define an unobstructed central area which allow fish to escape out the upstream end of the shell. Debris passes through the shell by means of gravity. Russian Patent No. 647397 discloses a screw blade in a conduit for diverting fish and debris.